There is a continuing interest among consumers for very small, lightweight communications products, such as cellular telephones, pagers, and lap top computers. Product requirements for these systems typically call for small low cost antennas. Microstrip antennas have been used to accommodate these small design requirements, because they can be fabricated using inexpensive printed circuit board technology. Over the years, many forms of microstrip antennas have been developed, the "patch" antenna being one of the most popular. FIGS. 1 and 2 show top and side views respectively of a typical patch antenna 100. Patch antenna 100 includes a rectangular shaped radiator element 102 disposed onto a substrate 104 over a ground plane 106 and coupled to a radio frequency (RF) feed 108.
The single rectangular patch 102 is characterized by a resonant electrical length (along length 110) characterized by equation: ##EQU1##
where c is the speed of light, f is the resonant frequency, and .epsilon..sub.r is the dielectric constant of the substrate. However, the prior art antenna radiates in only one hemisphere away from the ground plane.
An example of an antenna which radiates in more than one hemisphere is the loop antenna, however, a loop antenna typically sits perpendicular to the product surface or suffers the consequences of being detuned.
It would be advantageous to have a microstrip antenna that could provide radiation coverage in both hemispheres. Such an antenna would be beneficial in both portable communications products and infrastructure apparatus.